When the lady comes to my motel room, is it okay to answer the door in my birthday suit or is that too forward? I just thought it might set the mood that I'm "ready to have fun!".

A little modesty would be of benefit to you if you really want a good time. Otherwise, she will think that you are a blatant, obnoxious asshole!

A nice pr. of slacks or dress shorts with a nice casual shirt will work well.

. . . they would turn around and walk away. So don't do it.

I agree with those already posting.... a "Birthday Suit" is not usually a good indication to me that a gentleman will synch with me. As someone suggested... at least a robe. (my .02 cents) ~T